Journal of Avian Biology最新文献

Factors outside the breeding season can affect population trends for migratory species. Yet information on population-specific migration and nonbreeding ecology for most species is lacking, complicating conservation efforts. Louisiana waterthrush Parkesia motacilla and worm-eating warblers Helmitheros vermivorum are Nearctic–Neotropical migratory songbirds that share breeding habitat associations, and occur in sympatry throughout most of their breeding distributions. Yet these species exhibit variable regional population trends on the breeding grounds, suggesting that processes outside of the breeding period may impact population growth. We used light-level geolocators to track Louisiana waterthrush and worm-eating warblers from four sites spanning their breeding distributions (Arkansas, Tennessee, Ohio, and Pennsylvania, USA). We describe the geographic distribution of populations during the nonbreeding period and quantify interspecific variation in the timing of migration to assess the potential for factors outside the breeding period to impact population dynamics. From 2016 to 2020, we marked 153 individuals (85 Louisiana waterthrush and 68 worm-eating warblers) across the four sites, and estimated migration timing, nonbreeding locations, and migratory connectivity for 24 Louisiana waterthrush and 21 worm-eating warblers. We observed moderately strong migratory connectivity (MC) in both species (Louisiana waterthrush MC = 0.40 [0.25 SE], worm-eating warbler MC = 0.44 [0.13 SE]) between breeding and nonbreeding sites, and a high degree of overlap (i.e. > 50%) among most populations' nonbreeding core-use areas. Moreover, populations experienced largely similar environmental conditions (measured by enhanced vegetation index) during the nonbreeding period. On average, Louisiana waterthrush initiated migration ~ 40 days earlier than worm-eating warblers across the annual cycle, and this trend was strongest in southern breeding populations. These findings emphasize the value of leveraging multiple species into full-annual cycle studies to identify when and where factors limiting populations of migratory species may occur. Additionally, we demonstrate that migratory species that co-occur during stationary periods of the annual cycle (i.e. breeding and nonbreeding periods) can experience strong temporal isolation during seasonal migration.

Avian haemosporidians are a diverse group of parasites that infect birds worldwide and have been a major focus of research for decades. Yet, few studies have identified the drivers of infection at the intraspecific host level. We aimed to study the drivers of prevalence and diversity of haemosporidian parasites infecting a common North American songbird species, the American robin Turdus migratorius, which breeds across most of the continent. We found little seasonal variation in haemosporidian prevalence in robins, although we detected a significantly positive relationship between robin breeding latitude and co-infection with different haemosporidian parasite lineages. Additionally, robins infected with Plasmodium had substantially better body condition than uninfected robins, which could be due to migratory culling. We detected 31 haemosporidian lineages among the robins we sampled, of which eight were novel. When matched against known haemosporidian lineages, our results suggest that robins harbor a higher diversity of haemosporidian parasites than previously known. The results of this study suggest that comparisons of common, widespread bird species such as robins across their range could help unveil novel aspects of the haemosporidian–host relationship and how such a relationship may change under current and future rapid environmental change.

The Australian zebra finch is an arid-adapted passerine with high hygric demands, that is projected to be at risk from increasing temperature and aridity throughout its distribution by the end of the century. We examine here how individual zebra finches modify their visits to water in response to the climatic conditions of ambient temperature, relative humidity, rainfall, wind speed and day length over a two-month period during an Austral summer drought in arid central Australia. Visits to water by individual zebra finches increased with increasing ambient temperature and day length, and decreased with increasing relative humidity, wind speed and rainfall. These findings are the most comprehensive data for the pattern of visits to water by individual wild birds globally and highlight the importance of regular drinking by individual finches to maintain water balance and thermoregulation. Our data highlight the importance of water availability for birds in the arid zone in a warming climate.

Hover-feeding by hummingbirds from pendent flowers relative to horizontal flowers increases the metabolic cost of flight, but in nature a large proportion of hummingbird-pollinated flowers are nonetheless oriented near-vertically downward. We used binary-choice tests to assess behavioral preference of captive Anna's hummingbirds for these two particular floral orientations. The extent of nectar consumption from artificial flowers differed significantly over a 2-hour exposure period, with birds showing greater extraction from the horizontal configuration. We also found that time spent hovering at the feeder immediately prior to nectar extraction did not vary by feeder orientation, whereas feeding duration tended to be greater at horizontal feeders. Opportunistic measurements of wild hummingbirds were also consistent with a preference for horizontal feeders. In aggregate, these observations suggest that the increased metabolic cost of hover-feeding from pendent flowers is matched by an associated behavioral aversion, at least under the conditions examined here. However, pendent hummingbird-specialized flowers are common, suggesting that additional behavioral or ecological factors underpin evolutionary persistence of this floral presentation.

Phenological changes are one of the most well recognised responses of organisms to climate change. The ability to detect phenological change often relies on long-term datasets, which are scarce in the Southern Hemisphere. As the adaptive capacity of species is highly variable, it is important to better understand how species in the Southern Hemisphere may respond to climate change through shifts in their annual cycles. Citizen science projects, like bird nest record schemes, offer valuable long-term data, although data heterogeneity can pose challenges, affecting their use in research. To investigate the suitability of the South African nest record scheme (SANRS) for estimating phenological shifts, we conducted a preliminary exploration of shifts in lay dates in four well-represented species. Firstly, we explore the composition of nest cards for each species, specifically the proportions of single- and multi-visit cards. Secondly, we explore the accuracy of single-visit cards for estimating lay dates compared to more accurate multi-visit cards. Lastly, we compared analytical approaches to test for possible shifts in lay dates. We found little differences for lay date estimates between single and multi-visit cards and our different models showed similar patterns of lay date shifts for all species. Three of our four species (African paradise flycatcher Terpsiphone viridis, cape turtle dove Streptopelia capicola, cape wagtail Motacilla capensis and laughing dove Spilopelia senegalensis) showed a shift toward later laying over the period 1950–1999. Although only based on a limited number of species, this consistent pattern towards later lay dates contrasts with the general trends found in the Northern Hemisphere for shifts toward earlier laying. The mechanisms driving these shifts is currently unclear, but in contrast to the Northern Hemisphere, in this region rainfall rather than temperature may have a stronger influence on avian breeding phenology. Our results highlight the potential of the South African Nest Record Scheme to detect shifts in laying dates, paving the way for more extensive studies of phenological changes, and the mechanisms involved, in the under-researched region.

Same-sex sexual behaviour (SSB), encompassing actions such as courtship, pair bonding, and parenting between individuals of the same sex, has been observed across numerous taxa, including birds. Yet despite its widespread occurrence, SSB remains poorly understood, often dismissed as maladaptive or the result of errors in sex discrimination. However, instances of same-sex partnerships – persistent pair bonds between same-sex individuals – challenge these assumptions, particularly in birds, whose diverse mating systems and high level of monogamy imposes strong selective pressures on pair formation and maintenance. This review synthesises our current knowledge of same-sex partnerships in birds, addressing their evolutionary origins, adaptive benefits, and broader ecological significance. We argue that the prevalence of same-sex partnerships has likely been underestimated, hindered both by historical biases in interpretation and, especially more recently, logistical challenges in data collection. Drawing on examples from across the avian class, we explore the potential reproductive and social benefits of same-sex partnerships. By reframing these behaviours as potentially adaptive rather than anomalous, we aim to advance understanding of their evolutionary persistence and encourage more systematic research into their occurrence and implications.

Feather structure contributes greatly to a birds' ability to repel water, which is essential for thermoregulation and energy use. Water repellency of feathers has traditionally been inferred by measuring a structural index based on the distance between the feather radii and vane. A more direct method measures the contact angle of a water droplet resting on the pennaceous vane. This method is used for measuring the water repellency of various materials (e.g. textiles) and we considered it a standard against which the structural index can be validated. Despite widespread use of both techniques, their level of agreement with each other has not been systematically evaluated. Additionally, few studies have tested the direct contribution of uropygial oil to a feather's water repellency. We tested the correlation between the two methods, using feathers from two high-elevation species that are adapted to the cold and wet conditions of montane systems, Swainson's thrush Catharus ustulatus and Bicknell's thrush C. bicknelli. We also compared contact angles measured on feathers before and after removing their coating of uropygial oil. We found no correlation between the methods in either species, which suggests the structural index is not a reliable indicator of feather water repellency. Removing uropygial oil significantly reduced contact angles in both species, demonstrating a direct contribution of the oil to water repellency. The lack of agreement between the structural index and contact angle method may have occurred because the structural index infers water repellency by proxy, whereas the contact angle method more directly measures the degree to which a feather repels water. We consider the contact angle method to also be more standardizable than the structural index, although it requires more sophisticated equipment. We caution against continued use of the structural index and highlight the direct role of uropygial oil in enhancing feather water repellency.

As day length increases in spring, birds prepare to migrate and breed, relying on timing mechanisms shaped by selection to match their behavior and physiology to ecological conditions suitable for reproduction. As the climate changes these mechanisms will determine how successful birds will be in keeping up. In this contribution, we review studies comparing photoperiodic thresholds, endocrine profiles of testosterone and corticosterone, and gene expression during pre-breeding in seasonally sympatric migratory and resident populations of a songbird, the dark-eyed junco Junco hyemalis. Elevation of testosterone in response to GnRH served as a proxy for gonadal development, visible fat served as a proxy for migratory state, and stable isotopes in feathers and claws served as a proxy for breeding and non-breeding latitudes. Living in the same pre-breeding environment, migrants prepared to migrate by fattening and delaying gonadal development, while residents initiated gonadal development while not fattening. Within migrants, estimated latitude of origin co-varied positively with fattening and negatively with gonadal development. Together these mechanisms likely serve to match timing of migration and reproduction to the future appearance of favorable environments where breeding will occur. Differences observed in the wild persisted in a common environment, suggesting genetic divergence and local adaptation, though the possibility of early developmental effects on timing remain. As the climate warms and resources to support reproduction appear earlier, locally adapted dispersing immigrants from lower latitudes may bring along their earlier timing thus providing genetic or developmental rescue. Future research on mechanisms responsible for variation in timing among populations will allow better predictions of how adaptation to climate change will unfold.

Keywords: common garden, dark-eyed junco, gonad, hormone, local adaptation, migration, phenology, photoperiodic threshold, stable isotope

Ecologically relevant factors such as exercise and diet quality can directly influence how multifaceted physiological systems work; however, little is known about how such factors directly and interactively affect key components of the antioxidant system in multiple tissues of migratory songbirds. We tested 3 main hypotheses across three tissues in European starlings fed diets with more or less antioxidants (anthocyanins) and long-chain omega-6 polyunsaturated fats (18:2n6) while being flight-trained in a wind tunnel. Stimulatory effect of flight: flight-training stimulated the antioxidant system in that 1) plasma oxidative damage (dROMs) was reduced during a given acute flight, and contrary to our predictions, 2) antioxidant capacity (OXY or ORAC) and oxidative damage in plasma (dROMs), flight-muscle, and liver (LPO) of flight-trained birds were similar to that of untrained birds (i.e. not flown in a wind tunnel). Flight-trained birds that expended more energy per unit time (kJ min⁻¹) during their longest, final flight decreased antioxidant capacity (OXY) the most during the final flight. Dietary fat quality effect: contrary to our predictions, dietary 18:2n-6 did not influence oxidative status even after flight training. Dietary antioxidant effect: flight-trained birds supplemented with dietary anthocyanins did not have higher antioxidant capacity in plasma (OXY), or liver and flight-muscle (ORAC) compared to untrained birds. Counterintuitively, oxidative damage (dROMs) was higher in flight-trained supplemented birds compared to unsupplemented birds after an acute flight. In sum, the antioxidant system of songbirds flexibly responded to changes in availability of dietary antioxidants as well as increased flight time and effort, and such condition-dependent, individual-level, tissue-specific responses to the oxidative costs of long-duration flights apparently requires recovery periods for maintaining oxidative balance during migration.

Wolverton, H. and Anderson, R. C. 2024. Syntax in animal communication: its study in songbirds and other taxa. J. Avian Biol. 2024: e03258. https://doi.org/10.1111/jav.03258.

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